Need some expertise - this is a weird one for me.
1997 F150 with factory tow package , rear trailer plug.
ONLY the passenger brake light doesnt work; everything thing else does. Bulb is good, swapped it out with the drivers side.
No obvious rubs or pinched wires .
Did I miss something?

 

The right stop / turn on the trailer tow adapter does not work ?

Did you swap the left & right stop / turn relays to make sure the problem stays with the side or moves with the relay ?

 

This is the troubling part: turn signals work on both sides, running lights work on both ides, JUST the passenger brake light doesnt work.

 

I cant drive this truck because I only have one operational brake light and I cant afford a ticket right now. There has got to be someone who has run accross this before.
If it were a fuse or relay, why does the brake light only work on one side only?
If you were a Ford Tech, where would you start?

 

So it is the truck not the trailer tow adapter ?

How are you checking the turn signal operation via the actual turn signal or the hazards ?

 

thanks for the reply. the Truck doesnt have the passenger brake lite, Both the driver and turn signals both work fine when I get in the truck and operate the left and right turn signals.

 

I believe that could be the brake switch. Hazards and turns work but brake lite doesn't. I would pull the bulb and use a lite tester with a helper and see if you are getting power at the socket. I tried to find a diagram but no luck yet. a member named hawkeye seems to have alot of knowledge about this stuff.

 

I disagree. If it was BOTH rear brake lights that didnt work, but its only ONE. How does the brake switch know left from right?
There is power to the socket for the running/tailight but NOT for the brake light one the ONE side.
Hows that for a mystery?

 

I am going to take a SWAG at this point, and say the neutral position - contacts in the MFS could be the issue.

This is what the brake lamps route through, if a turn signal is not on ( stop lamp feed through in the chart below ).

Try cycling the hazard switch 6 or 10 times, to see if it changes it ( some times this will clean the contacts ).
If not, you are going to have to tear into the steering wheel column cover to test the switch.

It does not act like the MFS connector being pulled apart, considering the turn part works.



Here is a thread that JMC describes taking the key cylinder out, so you can get the top cover off ( without playing the pry and pray game ),

https://www.f150online.com/forums/el...beep-beep.html

The stop lamp feed through is the neutral position, where the output of the Brake Pedal Position switch ( or Brake On Off depending on who you ask and truck age ) is routed to both rear tail lamps.

This in OK up to the split from terminal #9 on the MFS.
The issue is inside the MFS, the terminal #2 to the common to terminal #9, this is the contact I think is dirty, and maybe a few hazard switch cycles might take care of it ?? Just a SWAG, could save you taking it all apart.

 

I now have a tendency to believe SSCULLY is correct. The wiring diagram shows that a bad contact or sticking contact is a likely culprit. A replacement MultiFunction Switch MFS is not a terribly expensive component ($40-$60.) Im not quite sure what is involved in replacing this on a 1997 F150, but I have replaced one on an older GM column.
Thanks for the wiring diagram. Great diagnostics!!

 

The post above JMC explains removing it.

the bottom cover is 3 screws and it drops down.

the 4th hole for a nails set or drift ( and the correct key position ) and the key cylinder comes right out. This makes taking the top straight up an easy task.

Once you get to that point, you are looking at the MFS.

This is supposition on my part, and most places will not take back electrical items, so without testing this could result in parts.

Just something to keep in mind, but if a new MFS does not cure it, I have no clue where to look next, considering the left and the CHMSL are working correctly.

 

Ok, lets say for now you're a genius, as your SWAG was correct! Let other members who are in a similiar situation learn from this. Here's what happened: I turned on the four way flashers and then the turn signal on the passenger side flashed rapidly briefly and then the four ways started working. I did this same process several times. Finally, the four ways came on without the turn signal. I then checked the brake lights and they BOTH worked.
Go ahead and install the MFS anyway? I think I'll wait.
Thanks again!